Near Space
by L. Paul Verhage
Approaching the Final Frontier
Near Space
Experiments for Your Near Spacecraft
Now that you have a near
space(NS) craft, what
experiments can you
perform with it? Since it has a simple
tracker — not a flight computer —
there are some limitations. There
are many experiments that function
on their own; however, before you
can process your science results,
you need to understand the format
of the data transmitted by the Tiny
Trak 3 in your NS craft.
The Tiny Trak 3 posit contains a
time stamp that is not found in the
posits of the Tiny Trak 2. The time
stamp is very useful when analyzing
your data. There is a way to get
around this that we’ll cover at the
end of this month’s column.
A Sample Tiny Trak
3 Output
Tiny Trak 3 Data
Format
F
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r
E
l
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c
t
r
o
n
i
c
s
NUTS & VOLTS
E
v
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t
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g
The Tiny Trak 3 is a PIC-based
radio modem, although it might be
better to call it an MO, since it does
not demodulate radio transmissions.
When programmed for amateur NS
use, the Tiny Trak 3 uses data fields
from two GPS sentences —
the GPGGA and GPRMC.
Elements from both
sentences are combined into
the Tiny Trak 3’s posit. You
can think of a posit as a
condensed position and status
report. As such, a Tiny Trak
3 posit contains enough
data for you to perform
some amateur science
without carrying anything
else inside of your NS craft.
The older Tiny Trak 2
works well as the NS avionics, but you should consider
at least replacing its PIC
microcontroller with the
newer Tiny Trak 3 version.
Example 1 shows the highest
altitude posit received from one of
my NS craft during a mission last
year.
On this particular mission, my
module transmitted posit reports
every 60 seconds. The mission’s
science data was stored onboard for
retrieval after recovery. This method
of storing science data onboard has
several benefits. For one, my important
science data is not contaminated
with packets from local hams and
chase crews. Believe me, it can take
several hours to clean up an APRS
log. The second benefit is that there
are no dropped packets to contend
with. APRS is designed to be a
robust communication method;
however, packets are only transmitted
once and there is no verification
that they were received (this is
important to consider, since the
receiver is usually a moving target).
As a result, posits are occasionally
not received on the ground. This is
not a problem for determining the
landing zone of the NS craft, as
there are still plenty of received
posits, but, if you’re sending science
data over APRS, the missing data
can be a real aggravation.
The Tiny Trak 3, safely anchored in its reusable
lunchbag near space module.
Format of the
Tiny Trak 3
So what does the
sample posit say? The posit
from the Tiny Trak 3 uses
the following format:
callsign, routing information,
time, latitude, longitude,
direction, speed, and altitude.
90
The FCC (Federal
Communications
Commission) issues you a
callsign after you earn your
amateur radio license. The
callsign is unique to you
and is used for identification.
MAY 2004
